Final Comprehensive Conservation Plan - U.S. Fish and Wildlife ...

Hakalau Forest National Wildlife Refuge
Comprehensive Conservation Plan
Some mechanical control methods (e.g., mowing), used in combination with herbicides, can be a
very effective technique to control perennial species. For example, mowing perennial plants
followed sequentially by treating the plant regrowth with a systemic herbicide often would
improve the efficacy of the herbicide compared to herbicide only treatment.
• Cultural Methods. These methods would involve manipulating habitat to increase pest
mortality by reducing its suitability to the pest. Cultural methods could include water-level
manipulation, mulching, winter cover crops, changing planting dates to minimize pest impact,
prescribed burning (facilitate revegetation, increase herbicide efficacy, and remove litter to assist
in emergence of desirable species), flaming with propane torches, trap crops, crop rotations that
would include non-susceptible crops, moisture management, addition of beneficial insect habitat,
reducing clutter, proper trash disposal, planting or seeding desirable species to shade or outcompete
invasive plants, applying fertilizer to enhance desirable vegetation, prescriptive grazing,
and other habitat alterations.
• Biological Control Agents. Classical biological control would involve the deliberate
introduction and management of natural enemies (parasites, predators, or pathogens) to reduce
pest populations. Many of the most ecologically or economically damaging pest species in the
United States originated in foreign countries. These newly introduced pests, which are free from
natural enemies found in their country or region of origin, may have a competitive advantage
over cultivated and native species. This competitive advantage often allows introduced species
to flourish, and they may cause widespread economic damage to crops or out compete and
displace native vegetation. Once the introduced pest species population reaches a certain level,
traditional methods of pest management may be cost-prohibitive or impractical. Biological
controls typically are used when these pest populations have become so widespread that
eradication or effective control would be difficult or no longer practical.
Biological control has advantages as well as disadvantages. Benefits would include reducing
pesticide usage, host specificity for target pests, long-term self-perpetuating control, low
cost/acre, capacity for searching and locating hosts, synchronizing biological control agents to
hosts’ life cycles, and the unlikelihood that hosts will develop resistance to agents.
Disadvantages would include the following: limited availability of agents from their native
lands, the dependence of control on target species density, slow rate at which control occurs,
biotype matching, the difficulty and expense of conflicts over control of the target pest, and host
specificity when host populations are low.
A reduction in target species populations from biological controls is typically a slow process, and
efficacy can be highly variable. It may not work well in a particular area although it does work
well in other areas. Biological control agents would require specific environmental conditions to
survive over time. Some of these conditions are understood; whereas, others are only partially
understood or not at all.
Biological control agents will not completely eradicate a target pest. When using biological
control agents, residual levels of the target pest typically are expected; the agent population level
or survival would be dependent upon the density of its host. After the pest population decreases,
the population of the biological control agent would decrease correspondingly. This is a natural
cycle. Some pest populations (e.g., invasive plants) would tend to persist for several years after a
G-6 Appendix G. Integrated Pest Management